1. Field of the Invention
The present invention relates to a bearing part for a cylindrical roller bearing and a needle roller bearing. By applying the bearing part to a rolling raceway surface of a roller of the cylindrical roller bearing or needle roller bearing, it is possible to extend the life of the rolling raceway surface of a roller of the bearing part of the cylindrical roller bearing or needle roller bearing.
Moreover, the bearing part is formed with a surface layer having a retained austenite of about 30%. The surface layer is subjected to a specific heat treatment for applying a residual compression stress. Thereafter, surface layer is subjected to specific surface machining so that the surface is formed with micro concavo-convex portions in a random direction. Then, a cylindrical roller bearing or needle roller bearing having a long life roller are used in combination with these bearings. This procedure makes it possible to achieve a long life of the entire bearing structure comprising the bearing part and the cylindrical roller bearing or needle roller bearing.
2. Description of the Related Art
In order to achieve a long life of the entire bearing structure comprising a cylindrical roller bearing or needle roller bearing and a bearing part having a rolling raceway surface of a roller of the bearing, both the roller of the bearing and the raceway surface must have a long life. Otherwise it is impossible to achieve a long life of the entire bearing structure.
In order to extend the life of the cylindrical roller bearing or needle roller bearing, for example, Unexamined Patent Publication (Kokai) No. 5-239550 has disclosed a roller for a cylindrical roller bearing or needle roller bearing, having a longer life than in the conventional case. This is achieved by improving a retained austenite amount of a surface layer by about 30%, and subjecting the surface layer to a specific heat treatment for applying a residual compression stress. Thereafter, the part is subjected to specific surface machining so that the surface is formed with micro concavo-convex portions in random directions.
However, in the bearing part used as a rolling raceway surface of the roller of the cylindrical roller bearing or needle roller bearing, conventionally, a case hardened steel is subjected to a carburizing treatment. Thereafter, the surface is merely subjected to finishing so as to have an accuracy (i.e., deviation from circular form, cylindricity (deviation from cylindrical form), surface roughness) enough to function as a rolling raceway surface of the roller.
For this reason, even if the cylindrical roller bearing or needle roller bearing having the aforesaid long life roller is used, the bearing part used as a rolling raceway surface of the roller remains the same as in the conventional case. Thus, the life of the rolling raceway surface of the roller of the bearing part is deteriorated. This limits the life of the entire bearing structure. As a result, there is a problem that the aforesaid roller having a long life is not effectively used.